The possible role of cis-trans isomerism in protein denaturation reactions is being studied with the idea that this may be the rate-limiting step in folding and unfolding reactions. Members of the family of Ca ion binding proteins from carp muscle are being isolated and studied, since some of these proteins have no prolines and some have one. Relying heavily on differential heat capacity calorimetry, lipid and protein transitions in erythrocyte membranes, mitochondrial membranes and chromaffin granule membranes are being studied. In the case of the erythrocyte membrane, two lipid-related transitions have been found and characterized with respect to their sensitivity to pH, salt concentration, and other physiological solutes.